The present invention relates to a torque converter generally used for a motor vehicle, and more specifically to an oil passage system of a lockup torque converter.
FIG. 2 shows a conventional torque converter (as disclosed in Japanese Utility Model Provisional Publication No. 62-162448. The torque converter 10 shown in FIG. 2 includes a pump impeller 12, a turbine runner 14, a stator 16, a lockup clutch piston 18, a cover shell 20, nuts 22, a stator shaft 24, a one-way clutch 26, a hub 28, a turbine shaft (transmission input shaft) 30, a sealing ring 32, springs 34, a clutch facing 36, a release chamber 40, an apply chamber 42, an axial center hole 44, a converter sleeve 45, and a bushing 46. The lockup torque converter 10 functions as a hydrodynamic drive when the oil is supplied to the release chamber 40, and the oil flows therefrom to the apply chamber 42. The lockup clutch piston 18 is engaged to provide a direct mechanical drive when the oil pressure is supplied to the apply chamber 42, and the release chamber 40 is drained.
In the engaged state, however, the fluid pressure in the apply chamber 42 is liable to decrease because of leakage of the oil, and to cause slippage of the lockup clutch piston 18. The oil pressure is supplied to the apply chamber 42 through an annular passage 47 between the converter sleeve 45 and the stator shaft 24 while the release chamber 40 is drained through the axial hole 44 of the turbine shaft 30. In this case, a clearance 48 between the stator shaft 24 and the turbine shaft 30 is put in the drain state because the clearance 48 is in communication with the axial hole 44. Therefore, one side of the bushing 46 receives the oil pressure in the apply chamber 42 whereas the other side is held in the drain state. The thus-developed pressure difference across the bushing 46 incurs leakage of the oil through the clearance between the bushing 46 and the turbine shaft 30, which results in a decrease of the oil pressure in the apply chamber 42, and a decrease of the force pressing the lockup clutch piston 18 against the cover shell 20.